In the 1st place you should not use this kind of filter.......don't think it can handle the waste generated by the fishload and what ever you keep in the tank.
This is more for fresh water as the fishes are more tolerant of high nutrient level and water change is relatively easy.
Since you are using it, you can put what ever inert filter media you want......filter media are almost the same for marine or fresh. It just a substrate for the denitrifying bacteria to grow.